This invention relates generally to clutches. More particularly, it relates to a clutch for use in effecting locking engagement between a front drive axle and a front wheel of a four-wheel drive vehicle in response to the application of power to the front drive axle. The clutch automatically effects disengagement upon cessation of the application of power to the front drive axle, together with a direction reversal.
Heretofore, various clutching mechanisms have been used for engaging a front drive axle with its associated wheels in a four-wheel drive vehicle. One such mechanism normally is disengaged to allow the wheels to rotate independently of the front drive system. This requires that the operator lock each clutch manually to engage the front drive axle and wheels, and to unlock them manually to disengage.
Another such mechanism provides an overrunning clutch which engages automatically when power is applied to the front drive axle and when operation is in the drive mode. However, such an overrunning clutch disengages automatically upon operation in the coast mode. In other words, the overrunning clutch engages when the rotational speed of the axle tends to exceed the rotational speed of the wheel, but disengages when the rotational speed of the wheel tends to overrun that of the axle. Such overrunning clutches generally provide some means by which the operator may override manually to insure locking engagement between the axle and wheels.
Yet another such mechanism provides a clutch which operates in response to the application of torque to the front drive axle to move pins into slots so as to engage the axle with its associated wheels. Although a mechanism of this type will effect engagement in either the drive or coast mode of operation, there is the possibility that the pins will slip out of the slots during movement between drive and coast, in which case the clutch would disengage and then re-engage automatically. At normal operating speeds such disengagement and re-engagement could cause severe shocks to the clutch components and, indeed, to the entire front drive line. This would result in a dangerous and possibly destructive condition. Further, in a float condition wherein the axle is rotating but no torque is transferred between the axle and wheels, an inadvertent tendency for movement between the drive and coast modes of operation could develop. This could cause the clutch to disengage and then re-engage, and establish the same dangerous condition.
There remains a need in the art for a clutch which will automatically engage a front drive axle and an associated wheel in response to engagement of the front wheel drive system, which will maintain engagement positively in the drive and coast modes of operation as well as during the transition between drive and coast, which will maintain engagement positively in forward and reverse operation as well as during the transition between forward and reverse, and which will disengage automatically upon disengagement of the front wheel drive system.